In usability research, difference between formative and
reflective measurement models for the assessment of latent
variables has been ignored largely. As a consequence, many
usability scales are misspecified. This might result in reduced
scale validity because of the elimination of important usability
facets within the procedure of scale development. The aim of
the current study was to develop a questionnaire for the
evaluation of On-line store usability (UFOS-V2) that includes
both a formative and a reflective scale. 378 subjects participated
in a laboratory experimental study. Each participant visited two
out of 35 On-line stores. The usability and intention to buy was
assessed for both stores. In addition, actual purchase behaviour
was observed by combining the subjects' reward with the
decision to buy. In a two-construct PLS structural equation
model the formative usability scale was used as a predictor for
the reflective usability measure. Results indicate that the
formative usability scale UFOS-V2f forms a valid set of items
for the user-based assessment of online store usability. The
reflective usability scale shows high internal consistency.
Positive relationships to intention and decision to buy confirm
high scale validity.